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Lower mileage after cleaning throttle body and MAF sensor

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Phamburger, Aug 3, 2014.

  1. Phamburger

    Phamburger New Member

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    Hello. I drive a 2007 Prius with 75000mi. So dealership pointed out my throttle body was dirty and needed cleaning so I decided to do it myself. Before I cleaned the throttle body with CRC Throttle Body Cleaner and the MAF sensor with CRC MAF Cleaner, my avg mpg was ~48mpg on each tank. I read cleaning throttle body and MAF sensor will improve mpg by about 3-5mpg, but this was not the case. After I cleaned these two components, I am now averaging about 40mpg on the exact same conditions I've been driving under. In addition, my ICE remains running for a significantly longer time at stop lights before shutting off than before cleaning (shuts off after ~30sec-1min after coming to complete stop). Also, when I am going downhill now, I get about 75mpg because the ICE is also still running even with my feet off the acceleration pedal, whereas before it was displaying 99.9mpg on the same hill. I was thinking maybe something wrong with the throttle body now? Any explanations or help would be great. Thanks!
     
  2. edthefox5

    edthefox5 Senior Member

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    What did the dealer do to your car?

    You won't get any better mileage by cleaning the throttle body and I have never seen that mentioned here.

    Take the air cleaner box off and check all the hoses are connected. Take the big hose off the back of the tb and spray the cleaner through that port. That's the one that gets dirty as the big hose is the pvc hose. Check for free play with the butterfly by turning the springed end. Lubricate the springed end. I know the maf is plugged in because if it wasn't it would throw an instant dtc.

    Then when you put the air box assy back on make sure the throat clamp underneath the air box is tight also.
     
  3. Phamburger

    Phamburger New Member

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    The dealer didnt clean it. I did. I followed step by step instructions from diy prius to clean the TB and MAF sensor. I didnt take anything apart except remove the MAF sensor.
     
  4. Southbound

    Southbound Member

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    The dealer didn't do anything- he decided to do the job himself..

    ... day late and a dollar short..
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Please explain your exact procedure used to clean the throttle body and mass air flow sensor.
    2. In general, less is more when doing these cleaning procedures. This means you do not need to use 1/2 can of throttle body cleaning fluid and drown the intake manifold in cleaning liquid, to achieve a good result. The Toyota recommended procedure is to spray some cleaning fluid on a clean cloth and use that to scrub dirt off the throttle body interior and throttle plate, rotating the throttle plate shaft to gain access to the underside of the throttle plate. This avoids having dirty cleaning fluid laden with dirt getting into the throttle body motor shaft and binding the motor. Obviously the air cleaner housing has to be removed for access.
    3. The mass air flow sensor is cleaned by removing it from the air cleaner housing, and spraying the sensor bulb and bare wires with MAF cleaner. Do not touch any of those cleaned parts and make sure you have a good seal when reinstalling the sensor in the air cleaner housing.
    4. It is not reasonable to expect improved mpg by performing those cleaning procedures.
    5. The point of doing the throttle body cleaning procedure is to avoid engine no-start issues (DTC P3191 for example) which can happen if the throttle plate binds up.
    6. The point of doing the MAF sensor cleaning is to improve the engine ECU's ability to manage fuel delivery to the engine, and avoid a DTC being logged (such as DTC P0171, P0172, or one of the P010x codes.) That might result in a marginal mpg improvement but that should not be the primary motivator behind that cleaning activity.
    7. Make sure the wiring harness connector to the MAF sensor is properly engaged and locked.
     
  6. taylor_priusII

    taylor_priusII New Member

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    You killed the MAF.
     
  7. Phamburger

    Phamburger New Member

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    I followed this guide exactly:

    Toyota Prius: How to Clean the Throttle Body - PriusDIY.com

    Except instead of using a shop towel, I used regular paper towels and I think a very small bit of it (the size of a ladybug) ripped off during cleaning. I didnt think this would be a big issue since it would just burn off in the engine and disintegrate.

    On the cleaner bottles, it said spray liberally, so I used it pretty liberally and I could see fluid sitting at the bottom of the throttle body. As for the MAF sensor, I didnt touch any part of the bulb or wires, just sprayed it with MAF sensor cleaning fluid quite liberally as well.
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. It is not helpful for any debris to be allowed into the intake manifold. The concern is that the paper may stick to the edge of a valve, carbonize, and prevent the valve from sealing properly.
    2. What did the MAF sensor bulb and wires look like, after they were cleaned?
    3. At this point, if your car is not logging any warning lights, you should just drive it and perhaps the mpg will improve over time.
     
  9. Phamburger

    Phamburger New Member

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    The MAF sensor was a shiny, glossy amber after it was cleaned. The two wires were a shiny metallic silver. No warning lights were on and it runs fine, its just annoying to know my Prius isnt as quiet as it was before like a normal hybrid vehicle and im getting lower mpgs :[
     
  10. AzWxGuy

    AzWxGuy Weather Guy

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    I feel another guess coming on. The additional cleaning fluid in the bottom of the intake manifold has dissolved the oily residue that collects there and when ingested into the engine has temporarily fouled the plugs. It is more likely that the 12V battery has decided to give up the ghost in conjunction with this procedure. Working on your car with the windows down and your favorite radio station playing for 30 minutes or more (guessing here) might have been all it took. Excessive engine run times and a corresponding drop in mpg are a good indicator of a weak 12V auxiliary battery. Run this check and if the second voltage value is much below 12.0V you probably need a new battery.
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    A reasonable hypothesis, and the OP can prove or disprove this by removing the iridium spark plugs for inspection.
     
  12. Phamburger

    Phamburger New Member

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    Cant be the 12v battery since that was replaced 3 weeks ago with an Optima Yellow Top. I will try to remove the plugs when I get a chance and see if those can be replaced.
     
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Have you actually measured the 12V battery voltage? If not, you might be unpleasantly surprised: Prius won't run. | PriusChat
    See posts 5 - 7.
     
  14. Phamburger

    Phamburger New Member

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    It seems the more I drive, the ICE is turning off quicker and quicker at stops, although it's still long compared to before cleaning the TB and MAF. Maybe I'll just drive it out and the problem will fix itself in the long run if no one has an immediate easy fix to the issue.
     
  15. stonerider

    stonerider Member

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    I am reporting the exact same experience; I cleaned the MAF and TB yesterday using the CRC spray cans (MAF cleaner for MAF and TB cleaner for TB) and my Prius (2007 with 91K) doesn't turn ICE off as quickly as before. I didn't use paper to clean, I used a clean cloth to clean the TB. I did liberally spray the TB cleaner on the butterfly and underneath; no, I did not spray more than 5 or 6 times.
     
  16. valde3

    valde3 Senior Member

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    Ecu just needs to learn characteristics of changed throttle body. If it was dirty enough it may not even shut down engine at first. It learns it bit faster if you disconnect 12v battery for 10min to reset ecu. Or you can just drive it and it will eventually learn it.
     
  17. stonerider

    stonerider Member

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    I re-checked and re-tightened all the screws that I had removed/loosened for the job, found one screw that was loose, oops. Now, my Prius is back to normal. Thank you!

    Stone
     
  18. jeremnyc

    jeremnyc Junior Member

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    What about the non related MPG decrease as winter approaches? OP doesn't have a location listed.